WHITE BUTTERFLY PARASITE

Dominion, Volume 31, Issue 142, 12 March 1938, Page 8

WHITE BUTTERFLY PARASITE

Showing Signs Of Victory OVERTAKING SETBACK OF EARLY SUMMER ’ By Telegraph—Press Association. Palmerston North, March 10. Farmers throughout the Dominion will be encouraged by a report by Mr. C. J. Hamblyn, fields superintendent of the Department of Agriculture, that the parasite liberated to reduce the white butterfly is showing definite signs of victory over its host, which multiplied so rapidly this summer that about three weeks ago in the-Mount Stewart district it was possible to collect large quantities of the butterfly chrysalids. If the parasite had not been present, these would, within a few days, have hatched out as adult butterflies, ready to play their part in multiplying the petit. The parasite could be seen at work laying eggs in these chrysalids, but considerably more than 50 per cent, of the chrysalids had not been attacked and therefore would have produced butterflies. However, an inspection made a few days ago revealed a vastly different state of affairs. The parasite had apparently increased in numbers remarkably, and it was estimated that up to 90 per cent of the chrysalids had been attacked. This was forcibly demonstrated by the collection of some 500 chrysalids which were confined under glass. After three days only five butterflies emerged, whereas hundreds of parasites made their appearance. “It is more than probable,” said Mr. Hamblyn, “that throughout the southern half of the North Island where the white butterfly is continually reported to be doing considerable damage to crops of the turnip family, the parasite is present, and the same state of affairs as found in the Feilding district applies. This being so, it is not likely that further liberations of relatively small numbers of parasites would do any good at stage. Farmers interested would be well advised to. make a small collection of chrysalids and place them under .glass and watch for the proportion of parasites to butterflies hatching out. Failure of the parasite to overtake the butterfly in the ’early part of the season has not yet been accounted for. “The possibility of this parasite actually being reduced“by a parasite of its own has not been overlooked by Mr. J. Muggeridge, entomologist at the Cawthron Institute, where the work of breeding the parasite is 'being ,done, 'but up to . the present nothing of this nature has been found. It would appear that the exceptional weatherof last summer and autumn gave the parasite a greater check than the butterfly, and from . the very small numbers at the beginning of the season, it has taken some time to increase to the extent of overtaking the butterfly. which had everything in its favour for some/months. In all cases where control of the insect pest is maintained by a parasite, there is fluctuation in efficiency of the control.”